Critical bands are perceptual filters that detect and separate spectral peaks in complex sounds. Here, we show that the main properties of psychophysically defined critical bands, as measured in narrow-band noise masking tests (species-specific frequency dependence and intensity independence of the bandwidths), are present in single neurons of the mouse's central nucleus of the inferior colliculus. Bandwidths of critical bands amount to, on average, 3/8-1/3 octave related to the neurons' characteristic frequencies. They are not determined by the shapes of the neurons' excitatory receptive fields. The results support the view that frequency resolution in the auditory system is shaped to its perceptual level in the main nucleus of the auditory midbrain.